Choosing the best steel pulley starts with determining how you intend to use it. Countless sizes and functions exist, and some steel pulley models are designed for specific purposes. If, for example, you will be replacing the pulley on your garage door, you may need to contact the manufacturer directly to get the right part. You may also be able to take the old pulley to the hardware store to find one that is a similar size and features similar shaping and so on. The weight capacity of the pulley will have the biggest impact on its usefulness for you.
A steel pulley itself may feature a groove around its perimeter to help guide a chain, cable, belt, or rope. This is useful for certain systems, such as pulley lifts that are used to hoist large items off the ground, but these grooves can be problematic for other systems, such as some types of serpentine or drive belts in automobiles. If you are buying a steel pulley for an engine, you will need to consult the manufacturer to ensure you choose the right component for the job.
Just as important as the steel pulley itself is the frame in which the wheel is mounted. This frame will often hold much of the weight of items being lifted, or take on strain from a belt or chain system. Once again, you will need to take note of the weight capacity of the frame and pulley to ensure it will be sufficient for your needs. In some cases, the frame may feature bolt holes so the unit can be secured to a beam or other solid object. If you intend to mount the pulley for lifting or moving items, be sure the frame has such holes of an appropriate size for large bolts or screws.
If the movement of the pulley is especially important, you may want to choose a steel pulley with high quality and/or serviceable bearings. The bearings are mounted at the center of the pulley where the axle goes through the wheel, and they keep the wheel moving smoothly during operation. Sometimes these bearings can be re-greased or even replaced as they wear, making that particular pulley set-up especially versatile. In other cases, the bearings may be especially high quality, thereby preventing the need for maintenance or replacement. Sealed bearings keep dirt and grit away from the bearings themselves, extending the life of the bearings and potentially avoiding damage to the pulley.